Where it is necessary to obtain a temperature measurement and it is impractical or impossible to make direct contact with the material to be measured, infrared pyrometers are generally successful in taking the temperature measurements. However attempts to utilize infrared pyrometers in textile environments for measuring the temperature of a textile web in a textile web treating oven, most commonly a tenter frame, have met with little success. The textile oven atmosphere is filled with contamination and lint which distort the signal received by the pyrometer. Additionally, the contamination and lint can accumulate on the lens of the pyrometer and affect the calibration and sensitivity thereof. Further, the textile web (fabric)--though generally considered a black body--exhibits a range of openness, and the exact readings cannot be obtained if the optical path passes through the open areas of the fabric. Additionally, the temperature within the instrument can become high enough to exceed the maximum temperatuure specified for it.
According to the present invention, a sensing unit is provided that can be utilized in textile environments, particularly in association with a textile web treating oven, or tenter frame, and for the practice of a method of determining and controlling textile web temperatures in a textile web treating oven. According to the invention all of the problems associated with conventional sensors utilized in textile environments have been overcome, and the invention is capable of accurately determining (and controlling) web temperature in a textile web treating oven over extended periods of time.
An exemplary sensing unit according to the present invention is adapted to be associated with a textile web treating oven, or other adverse environment apparatus, containing a structure whose temperature is to be sensed. The unit includes an infrared pyrometer and a fan, in a housing containing and mounting the pyrometer and the fan. An exhaust tube communicates with the interior of the housing and extends outwardly therefrom in operative association with a sensing portion of the pyrometer. Filter connection means are provided on the housing for facilitating connection of a filtering element to the housing, and means are provided defining an air flow passageway in the housing from the filter connection, to the fan, past the pyrometer, and to and through the exhaust tube. The filter connection comprises a short tube, and a filter bag is mounted on the end of the short tube. A bracket mounts to the exterior of the housing and the bracket includes a rod-receiving opening formed therein for receiving a stationarily mounted rod to mount the housing on the rod. The rod-receiving opening preferably makes an angle of between about 5.degree. to 25.degree. with respect to the exhaust tube.
The sensing unit according to the invention is preferably provided in a textile oven-sensor combination. An oven, having an exterior wall, has means defining an opening extending through the wall from the exterior of the oven to the interior thereto. A tube, referred to as a through-tube to distinguish it from an exhaust tube associated with the sensing unit, extends through the opening from the interior to the exterior of the oven. A seal is mounted on the exhaust tube to seal it with respect to the outside air. A bracket assembly means is provided for mounting the housing to the oven wall exterior surface so that the exhaust tube extends from the housing, exteriorly of the oven wall, through the seal and into the through-tube. The bracket assembly means comprises a bracket mounted to the sensing unit housing, and a substantially horizontally extending rod fixedly mounted to the oven exterior wall and extending outwardly from the oven wall. The fixed rod is received by a bracket rod-receiving opening in the housing.
According to the invention a method of measuring and controlling textile web temperatures in a textile web treating oven utilizing the above-described sensing unit is provided. The method comprises the steps of: Passing an open textile web in a first generally horizontal direction through a textile oven, the web being disposed substantially in a horizontal plane. Providing an opening in the textile oven adjacent an area wherein the web passes through the oven (as, for example, where the web reaches peak temperature). Mounting an infrared pyrometer so that it is in operative association with the oven opening and so that the pyrometer is disposed at a viewing angle of between about 5.degree. to 25.degree. with respect to the horizontal, preferably about 10.degree.. Obtaining temperature reading and, in response to the temperature readings determined by the pyrometer, controlling oven temperature and/or other factors to maintain the textile web at a predetermined desired temperature when passing through the oven. The spectral range of the pyrometer is preferably selected so that it is between about 2.8-3.3 microns. The pyrometer is cooled by a continuous flow of cooling and purge air to maintain its temperature at an operable level, and to prevent contamination thereof.
In the past, when pyrometers have been utilized with textile ovens, it has always been thought that the angle of viewing should be at least 45.degree.. However according to the present invention it has been found that--contrary to the teachings of the art--such an angle of viewing is too large, causing the pyrometer readings to be influenced by the temperature of objects behind the fabric web, which objects are viewed through the inherent openings in the fabric. According to the present invention it has been found that when the viewing angle is between about 5.degree.-25.degree. the pyrometer is not influenced by objects behind the fabric, and true readings can be achieved. The tighter the textile web (e.g. denim and corduroy) the less critical the viewing angle becomes; however for open textile webs (e.g. conventional woven fabrics) a viewing angle of between about 5.degree. to 25.degree. is critical.